"It's very easy to say that the product is faulty instead of analysing what is going on with the installation," Meritxell Arnedo from the Spanish supplier Isotubi said.

She said other parts — including valves supplied by other companies — have corroded too, and is adamant the water is to blame.

"Of course sometimes it might be a manufacturing problem but in this case, it is very strange that different pipes, different sizes, different factories, different dates, different raw materials — all of them were faulty," she said.

Microscopic bacteria blamed

Ms Arnedo said the problem was due to microscopic bacteria in the water system, which had made its way into the water from the old pipes at QEII — a phenomenon known as microbial influenced corrosion (MIC).

Curtin University experts have carried out extensive testing of the pipes at Perth Children's Hospital and deemed the risk of MIC to be low, but conceded it was still poorly understood and recognised because it could look like other forms of corrosion.

Ms Arnedo said the same parts — manufactured in the same batch — were installed in other parts of the hospital, with a different water supply, and showed no sign of corrosion.

She said that was the case for other projects in Perth.

"The same pipes with the same batch number, with the same production number, have been installed in other jobs in Australia, have been just checked ... and they are perfect," she said.

Swinburne University biomedical engineering professor Scott Wade specialises in MIC, and said one of its hallmarks is the speed of corrosion.

"So where you're getting corrosion rates that can eat through a steel pipe in say six months or a couple of months where you'd normally expect it to take several years," he said.

Dr Wade said if MIC was affecting the pipes at the Perth Children's Hospital, the problem would need to be solved quickly.

"Otherwise it will spread throughout the rest of the system potentially and rather than having to just fix up one small area you're going to have to spend a a lot of money to completely refurbish the system," he said.

The State Government said the pipes were replaced by another company in March and were compliant.

But so far, they have not been examined internally to see whether they too are corroding.